Virus attachment to a cell-surface receptor is the first step of a successful infection. Recently, significant progress has been made in understanding the histo-blood group antigens (HBGAs) as potential receptors for human rotaviruses (RVs). Following our last submission of this application, we discovered a unique evolutionary path for RVs, which points to a new direction in studying their diversity and evolution. In this application we will perform further studies to elucidate the molecular basis responsible for divergence and determination of host ranges among members in this path. Knowledge gained from this project should lead to a better understanding of RV epidemiology, disease burden, and control and prevention strategies. Three aims will be fulfilled: 1) We will perform in vitro binding/blocking experiments, including glycan array analysis, to more completely characterize this evolutionary path and determine the molecular factors that control RV host range in attempts to identify targets for antiviral development; 2) we will perform field studies on specific populations to refie our understanding of how HBGAs act as receptors or host susceptibility factors in RV infection in children, with the aim of developing a better understanding of strain-specific host ranges for future vaccine development against RVs; and 3) we will perform structural studies of the receptor binding interfaces of major human RVs by NMR and mutagenesis studies to establish a molecular level understanding of how HBGAs act as receptors for RVs. Knowledge of these structures should prove valuable for antiviral design against RVs using in silico approaches. The proposed studies in this application will be performed via a multidisciplinary collaboration of researchers with expertise and a strong track record in virology, glycobiology, clinical/epidemiology/statistics, and structural biology. We have recruited new collaborators who have generated strong preliminary data and who have access to unique research facilities, which has further strengthened our application. We are confident that we will make rapid progress in advancing our understanding of RV receptors.